The Hickson Compact Group 40

NASA is celebrating the Hubble Space Telescope’s 32nd birthday with a stunning look at an unusual close-knit collection of five galaxies, called The Hickson Compact Group 40.
This menagerie includes three spiral-shaped galaxies, an elliptical galaxy, and a lenticular (lens-like) galaxy. Somehow, these different galaxies crossed paths in their evolution to create an exceptionally crowded and eclectic galaxy sampler.

Caught in a leisurely gravitational dance, the whole group is so crowded that it could fit within a region of space that is less than twice the diameter of our Milky Way’s stellar disk.

Though such cozy galaxy groupings can be found in the heart of huge galaxy clusters, these galaxies are notably isolated in their own small patch of the universe, in the direction of the constellation Hydra.

One possible explanation is that there’s a lot of dark matter (an unknown and invisible form of matter) associated with these galaxies. If they come close together, then the dark matter can form a big cloud within which the galaxies are orbiting. As the galaxies plow through the dark matter they feel a resistive force due to its gravitational effects. This slows their motion and makes the galaxies lose energy, so they fall together.

Therefore, this snapshot catches the galaxies at a very special moment in their lifetimes. In about 1 billion years they will eventually collide and merge to form a giant elliptical galaxy.

Image credit: NASA, ESA, STScI; Image Processing: Alyssa Pagan (STScI) Larger image